Sudden cardiac death (SCD) is death resulting from a cardiac arrest in which the heart unexpectedly and without warning ceases to function correctly. In most cases of SCD, the heart’s “electrical system” malfunctions – electrical impulses in the heart become rapid and chaotic; the lower ventricles of the heart are unable to continue pumping blood to the lungs, body and brain. Death can occur within minutes of the onset of cardiac arrest, and in people with no known diagnosis of heart disease. SCD is a problem of major health proportions and approximately 400,000 people every year in the United States die of unexpected sudden cardiac death in an emergency department or before reaching the hospital [1].
There are a large number of potential causes of sudden cardiac death. The most common cause of SCD is a heart rhythm disorder (arrhythmia) called ventricular fibrillation (VF) [2]. Many victims of SCD have underlying heart disease, although they may not be aware of it. In approximately 80% of deaths resulting from SCD there is evidence of underlying coronary artery disease (CAD) [3]. Scarring from a prior heart attack is found in two-thirds of victims [4]. [Top] The Reynolds Center at Johns Hopkins University seeks to unravel the questions surrounding why certain people are at higher risk for developing lethal arrhythmias that can lead to SCD. What do we know currently about the prevention and treatment of SCD? There are two approaches to the prevention of SCD – primary and secondary. The type of prevention used depends largely on the level of risk a patient has of experiencing a life-threatening event. Primary prevention seeks to eliminate risk factors that may lead to cardiovascular disease. This can include the promotion a well-balanced diet, regular exercise, and smoking cessation. It is also important to treat underlying conditions and diseases like high blood pressure and diabetes which may contribute to heart disease. Secondary prevention of SCD is focused on individuals who may have already experienced life-threatening events. Secondary prevention and treatment may include the placement of an implantable cardioverter defibrillator (ICD), medication, and catheter ablation (CA).
Implantable Cardioverter Defibrillator (ICD) - a small automatic, electrical device designed to detect and correct arrhythmias. An ICD device is implanted in patients that have suffered or are at risk of suffering lethal abnormal heart rhythms. In the 1970’s the ICD was conceived and developed by Johns Hopkins-affiliated faculty member Michel Mirowski, MD. The first human implantation and the initial clinical trial of ICD safety and efficacy were performed at Hopkins by Dr. Mirowski in collaboration with Dr. Levi Watkins in cardiac surgery. |
A major focus of the Johns Hopkins Reynolds Center is the identification of patients at risk for SCD, in an effort to deploy more effective primary prevention strategies in that population. Of particular interest are patients with a low ejection fraction and prior myocardial infarction, a group in which ICDs have been shown to prolong life [5]. Unfortunately, most patients who receive ICDs for such an indication do not actually require the device or benefit from it. We seek to determine who really needs an ICD, and who would be safe without one. For more information on ICDs from a patient perspective, the following article is very helpful: J.A. Reiffel and J. Dizon, The Implantable Cardioverter-Defibrillator Patient Perspective, Circulation 105: 1022 – 1024, 2002. Medications – are prescribed to control abnormal heart rhythms or treat secondary conditions that may contribute to heart disease or SCD. Some types of medications used include anti-arrhythmic, beta-blockers, and calcium channel blockers. Medications are sometimes used in conjunction with ICD device therapy. Unfortunately, some medicines can actually increase the likelihood of SCD even if prescribed originally to suppress arrhythmias. Catheter Ablation (CA) – a technique using radiofrequency energy to selectively destroy small areas of heart muscle thought to be the culprits in the abnormal electrical signals causing arrhythmias. This technique is also sometimes used in conjunction with ICD therapy. References: - Zheng Z-J, Croft JB, Giles WH, Mensah GA. Sudden cardiac death in the United States, 1989 to 1998. Circulation 2001; 104: 2158-63.
- Patient and Public Information Center, Sudden Cardiac Death, NASPE Heart Rhythm Society, www.naspe-patients.org, 2003.
- Huikuri H, Castellanos A, Myerbrug RJ. Sudden death due to cardiac arrhythmias. N Engl J Med 2001; 345: 1473-82.
- Sudden cardiac death, American Heart Association, www.americanheart.org, 2003.
- Moss AJ, Zareba W, Hall WJ, Klein H, Wilber DJ, Cannom DS, Daubert JP, Higgins SL, Brown MW, Andrews ML. The Multicenter Automatic Defibrillator Implantation Trial II Investigators. Prophylactic implantation of a defibrillator in patients with myocardial infarction and reduced ejection fraction. N Engl J Med 2002; 346(12):877-883.
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Arrhythmia – abnormal heart beat or rhythm. Cardiomyopathy – a disease or disorder of the heart muscle, sometimes of unknown cause (“idiopathic cardiomyopathy”). Cardiac arrest – a sudden cessation of cardiac function, resulting in loss of effective circulation. Ejection Fraction – a measure of the proportion of blood that is expelled by the ventricle with each heart beat. Ischemic Heart Disease – inadequate blood flow to the heart primarily due to fatty buildups in the coronary arteries. Myocardial infarction (MI) – commonly known as a “heart attack” where clogged or blocked blood vessels cut off the supply of blood to the heart. Source: Data from The American Heritage Stedman’s Medical Dictionary, © 2002 Houghton Mifflin Co., New York, NY, American Heart Association (www.americanheart.org), and NASPE Heart Rhythm Society (www.naspe-patients.org). Interested in definitions for other cardiology terms? Send us an email with your suggestions, or explore some of the authoritative sites in the Useful Links section.
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